Because the ECG signal bandwidth typically observed for clinical diagnosis is less than 75 Hz, sampling rates that range between 150 and 500 Hz are sufficient to support clinical interpretation or automated machine analysis. If a pacemaker (pacer) signal is added to the ECG signal, this sampling rate is no longer adequate for the pacer signal component because a significant portion of its energy is at frequencies greater than 250 Hz. Increasing the sampling rate in order to accommodate the pacer signal component would add significant cost and expense to all devices and systems processing and storing the increased flow rate and quantity of data.
Because the pacer signal component can be a relatively tall (up to 700 mV) and narrow (˜0.1-2 ms) impulse that either triggers infrequently on demand or fires approximately 60 times per minute, it also contributes significant low-frequency energy overlapping the bandwidth of the core ECG signal. This fundamentally limits the effectiveness of linear filtering techniques, even at higher sampling rates. Moreover, if the pacer is malfunctioning, it can fire asynchronous to the QRS complex, or fire synchronous to the QRS complex, but out of proper phase so that the pacer spike sits on top of the R wave, for example. Other practical challenges are that the signal can: (a) range in amplitude from a fraction of the QRS amplitude to 100 times larger, (b) have significant undershoot or overshoot (e.g., biphasic), and (c) have a relatively long (e.g., >40 ms) settling time.
Nevertheless, it is desirable to process (that is, either detect, remove, and/or estimate) an ECG signal with a pacer component without increasing the sampling rate, while minimizing pacer signal related distortion. For waveform analysis, it is desirable to remove the pacer signal component without significant distortion regardless of the amplitude, phase, and synchronicity of the pacer signal relative to the QRS complex. Otherwise, pacer signals could be misinterpreted for example, as abnormal premature ventricular contractions. Poorly removing the signal, on the other hand, could increase the probability of additional analysis error.